1. Field of the Invention
The present invention relates to an endoscope, and more particularly to an endoscope system including two endoscopes that are different from each other in viewing angle.
2. Description of the Related Art
Conventionally, an endoscope has been widely used in a medical field and the like. The endoscope is employed to observe organs and the like inside a body cavity by inserting an elongate insertion portion into the body cavity, and to operate various treatments by using a treatment instrument that is inserted into a treatment instrument insertion channel, if necessary. A bendable portion is provided at a distal end of the insertion portion, and an observation direction of an observation window on the distal end portion is changed by manipulating a manipulating portion of the endoscope.
A viewing angle of the conventional endoscope is, for example, 140° (degree), and an operator observes inside the body cavity by an observation image corresponding to the viewing angle. When the operator desires to observe a region outside the region corresponding to the field of view during the observation inside the body cavity, the operator can bend the bendable portion to observe such a region.
An endoscope with a viewing angle that is wider than the viewing angle of the conventional endoscope is proposed to observe a wider region. When, for example, a large intestine interior is observed, a desired observation image of a backside of a fold of the large intestine and the like may not be acquired only by bending a bendable portion of the conventional endoscope to observe the observation region. The endoscope with the wide viewing angle has an advantage in which a region necessary to be observed or treated is easily found since the region corresponds to the wide field of view (see Japanese Patent Application Laid-Open No. H4-102432, for example).
However, in the endoscope with the wide viewing angle, when a focal length of a lens thereof is set to be the same as a focal length of the endoscope with the conventional viewing angle, a subject region displayed on a screen by the endoscope with the wide viewing angle is observed to be much smaller than a subject region displayed on the screen by the endoscope with the conventional viewing angle. Further, the subject region displayed at a periphery portion of the screen by the endoscope with the wide viewing angle appears to be remarkably small. Therefore, a size of the subject region displayed on the screen when the endoscope with the normal viewing angle is used by an operator, who uses the endoscope with the normal viewing angle and the endoscope with the wide viewing angle, differs from a size of the subject region displayed on the screen when the endoscope with the wide viewing angle is used by the operator.
Furthermore, when the operator intends to observe the subject region by bringing a distal end of the endoscope with the wide viewing angle near to the subject region to minimize the difference between the size of the subject region, which is displayed on the screen, of when the conventional endoscope is used and the size of the subject region, which is displayed on the screen, of when the endoscope with the wide viewing angle is used, as much as possible after the conventional endoscope is used, an imaging position of the subject region exceeds depth of field at a near limit side of the endoscope with the wide viewing angle. Hence, the subject region imaged by the endoscope with the wide viewing angle is not focused, and a blurred image is displayed on the screen.